Summary The purpose of this K22 Career Development Award is to foster the career development of Dr. J. Richard Pilsner, an interdisciplinary molecular epidemiologist. A long-term research goal is to delineate the role of epigenetics as an intermediate step in the mechanistic pathway linking maternal and paternal environmental exposures to reproductive success and subsequent offspring health and development. As a newly appointed Assistant Professor, I have been provided the necessary facilities and resources to establish a robust high- throughput laboratory for epigenetic analyses tailored for large population-based studies. The objective of this K22 application is to establish a cohort study of 250 subfertile couples seeking in vitro fertilization to examine the association between paternal phthalate exposure, sperm epigenetics, and reproductive health. To this end, I have identified specific areas where additional development will enhance my success as an independent researcher. These include: 1) endocrine disruptor compounds (EDCs); 2) sperm biology and male reproductive health; 3) cohort and biorepository implementation and 4) epigenetic informatics and computational biology. Phthalates, an EDC, are ubiquitous environmental contaminants that are used in plastics and personal care products. Phthalate exposure is associated with a diverse set of reproductive outcomes, including male reproductive health, birth outcomes, and offspring neurodevelopment; however, a mechanistic understanding of these associations has not been clearly elucidated. Epigenetic reprogramming is essential for sperm maturation and represents a critical window of susceptibility to environmentally-induced epigenetic errors that may, in turn, influence reproductive health. Emerging animal and human data indicate that male reproductive health is associated with epigenetic dysregulation in sperm. Moreover, recent evidence indicates that epigenetic information retained in mature sperm is enriched at developmental and imprinted genes, signifying that epigenetic patterns in sperm may be important for embryonic development after fertilization. To achieve our research objectives, we will: 1) examine the relationships between paternal urinary phthalate exposure on sperm DNA methylation at imprinted genes and by Illumina's 450K epigenomic array; 2) examine the influence of paternal phthalate exposure on sperm quality and embryo development; 3) use statistical mediation to examine if sperm methylation is a pathway by which paternal phthalates influence sperm and embryo quality. This study is innovative because: 1) while many epigenetic studies in humans are hampered by DNA from mixed cell types (e.g., leukocytes), our study utilizes a single cell type - sperm germ cells; 2) it will provide, to our knowledge, the first human data on the association between phthalate exposure and sperm DNA methylation through the use of both targeted gene and epigenomic approaches; and 3) it may challenge the current dogma of reproductive health by providing novel data on paternal environmental contributions to reproductive success.